In this paper, the behaviors of single bubble in shear-thinning viscoelastic fluids were investigated using OpenFOAM. The volume-of-fluid method was used to capture the interface, and the Giesekus model was adopted for describing the rheological behaviors of shear-thinning viscoelastic fluids. The bubble cusp, negative wake and velocity jump phenomenons in viscoelastic fluids were obtained, and the effects of wall effect, mobility factor α and Weissenberg number ( Wi) on bubble behaviors were investigated. The results showed that the viscoelastic stress is the main reason for the formation of bubble cusp, the relaxation of polymer macromolecules leads to the formation of negative wake, and the negative wake may be the main reason for the velocity jump. The open angle θ of the negative wake decreases and the distribution region in the vertical direction increases with the increasing Reynolds number ( Re). As well as the magnitude of the maximum negative velocity increases with Re and appears further away from the bubble cusp. Moreover, decreasing the wall effect can accelerate the formation of viscoelastic stress and make the bubble cusp appear earlier. As the mobility factor α increases, the viscosity and viscoelastic stress of the fluid near the bubble decrease, this causes the terminal velocity of the bubble to increase. As the Wi increases, both the maximum velocity and terminal velocity of the bubble increase, and the time lag occur. The viscoelastic stress Τyy has a longer linear distribution at the tail of the bubble with Wi increases.
As an environmentally friendly energy recovery technology, microwave pyrolysis has huge development potential in sludge resource treatment. This paper comprehensively reviews the progress of microwave pyrolysis of sludge, focusing on the mechanisms and development status of microwave pyrolysis equipment. The effects of pyrolysis temperature, heating rate, microwave absorbers, sludge properties and catalysts on microwave pyrolysis efficiency and its products are also discussed. Finally, the differentiation compared with conventional pyrolysis is summarized. It is suggested that target products can be controlled directionally by changing the pyrolysis conditions and exploring the harmful products produced in the microwave pyrolysis process. Future research directions are proposed to help the subsequent extensive application of microwave pyrolysis technology in sludge treatment.
The motion of droplets in non‐Newtonian fluids is widely present in ubiquitous industrial processes. Understanding the droplet motion characteristics is important for optimizing the design of related processes. Here the progress in the research on the droplet motion characteristics in non‐Newtonian fluids is reviewed. The mechanism of droplet deformation in non‐Newtonian fluids were elucidated, the influence of different rheological properties on droplet shape was discussed, and the empirical correlations of droplet aspect ratio were summarized. Moreover, the dimensionless correlations of drag coefficient were discussed. There are relatively few drag coefficient correlations of droplets in non‐Newtonian fluids, while the correlation of drag coefficients of bubbles in non‐Newtonian fluids can provide some reference. Finally, the possible prospects for future studies of the subject were proposed.
The interaction of two parallel unequal bubbles in a viscoelastic fluid is investigated numerically using OpenFoam, the volume of fluid method (VOF) combined with a surface tension model to trace the gas-liquid interface, and the Giesekus model to characterise the rheological properties of the fluid. The numerical results are in good agreement with experimental results from the literature. The effects of bubble diameter, initial spacing between bubbles and rheological properties of the fluid on the rise, and separation and convergence of the two bubbles are investigated. The flow field properties and viscoelastic stress distribution around the bubbles are explored. As the bubble spacing increases, the maximum and terminal velocities of the two bubbles increase, and the relative positions of the bubbles change when they come into contact. As the relaxation time λ increases, the contact time of the bubbles decreases, and the small bubbles tend to have an inverted teardrop shape and the large bubbles have less deformation and no sharp tail. The relaxation time directly affects the accumulation of viscoelastic stress, leading to changes in the velocity of the bubbles at contact, and their maximum and terminal velocities increase. Bubbles in highly elastic fluids are more prone to negative wake phenomena.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.